This invention is in the field of security and access control, and the invention particularly concerns access to door locks and other situations wherein numerous mechanical keys fit a single or a group of locks and wherein there is a need to control the instances of opening each lock and in some situations to maintain a record thereof.
In the past, a number of electronic security features have been added to mechanical locks which use mechanical types of cylinders. In addition, locking elements controlled by electronic means have been disclosed in combination with non-mechanical types of tumblers, such as in Clarkson et al. U.S. Pat. No. 4,712,398. In some cases electronic elements have been added to mechanical elements requiring both mechanical and electronic elements to be present before granting access such as Spahn et al. U.S. Pat. No. 5,469,727. Some of the existing electronic systems have employed keypads, some have employed cards, some have had purely electronic, magnetic or optical access control devices, and some have employed mechanical keys equipped with electronic circuitry.
With respect to the present invention, distinction is made among purely electronic, magnetic or optical keys; mechanical keys equipped with electronic, magnetic or optical features; and mechanical keys which operate solely by mechanical bittings, whether those bittings be pin tumbler, dimples or other mechanical patterns.
A key comprised of purely electronic circuitry, magnetic or optical data storage for determining and granting access is an electronic key. In the use of such a key, the circuitry or recorded data is transferred to a reader associated with a lock, and the reader recognizes a pattern or code held by the key. The key does not carry any mechanical cut or bitting configuration needed for granting access even though the key holding the data or the pattern may be used for turning the lock. Keys of this type can be found in U.S. Pat. Nos. 3,797,936 (Dimitriadis), 4,209,782 (Donath et al.), 4,257,030 (Bruhin et al.), 4,620,088 (Flies), 4,659,915 (Flies) and 4,789,859 (Clarkson et al.).
Keys referred to as mechanical keys are those which activate a mechanical device, with a pattern of mechanical bittings, by direct contact with the interpreting device, i.e. the tumblers or other pattern-holding apparatus contained in the lock. In a typical pin tumbler lock, access is granted based on the depth and configuration of key cuts meeting the tumblers. In most cases, once proper alignment is established in the tumblers, the keyholder is able to turn the key to lock and unlock the locking device. However, in some cases of mechanical keys, a push or pull action may be necessary for locking and unlocking of the device. The tumblers mentioned above can be pin tumblers, lever tumblers, disk tumblers, rotary disk tumblers, slider tumblers, or combinations of several of these incorporated within the same lock. Examples of purely mechanical keys are found in U.S. Pat. Nos. 480,299 (Voight), 550,111 (Sargent), 564,029 (Sargent), 3,208,248 (Tornoe), 4,723,427 (Oliver), 4,732,022 (Oliver) and 4,823,575 (Florian et al.).
Examples of mechanical keys equipped with electronic circuitry, magnetic or optical data storage or optical recognizable features (xe2x80x9cmechanical/electronic keysxe2x80x99) can be found in U.S. Pat. Nos. 3,733,862 (Killmeyer), 4,144,523 (Kaplit), 4,326,124 (Faude), 4,562,712 (Wolter), 4,663,952 (Gelhard), 4,686,358 (Seckinger et al.), 5,245,329 (Gokcebay), 5,367,295 (Gokcebay et al.) and 5,140,317 (Hyatt, Jr. et al.). Such keys carry the secondary element, whether it comprises electronic circuitry or some other type of coded data or recognizable pattern, in addition to the key""s mechanically operating pattern or bitting. In some instances both mechanical and non-mechanical features of a key are used simultaneously.
A lock cylinder is the control mechanism which grants access to the lock. A mechanical lock cylinder is the control mechanism which grants or denies access to the lock based on the mechanical key being used. The mechanical configuration, i.e. the cuts on the key, has to match to the meeting mechanical configuration i.e. the tumblers of the cylinder before the key will turn in the cylinder and this turning motion will engage the latch or bolt mechanism of the lock via a cylinder cam or tail piece causing the locking or unlocking of the lock. The cylinder mechanism of the lock is generally a separate module which can be easily removed and replaced. In certain types of locks the physical characteristics of the cylinders and their receiving cavity is standardized so one brand cylinder will fit or replace another brand of cylinder. Mortise, locks using mortise (regular or removable core) or profile cylinders (eurocylinder) and rim locks using rim cylinders are good examples. The cylinder size and shape differ on bored door locks such as knob or lever locks, and deadbolt locks. Thus, one can separate the mechanical lock cylinders into two categories, those that are standard in size and shape, and those that are brand specific. With the standard cylinders one brand cylinder will replace another instantly without any modification to the lock, door or the cylinder.
There are several cylinder manufactures who specializes in making replacement cylinders which fit in other brands of locks. In some cases these are specialized high security cylinders increasing the security of the lock by offering sophisticated locking principles and key control. Also several lock manufacturers have recently started to manufacture non standard (brand specific) cylinders that fit to their competitors"" locks. This is generally a marketing issue wherein by making cylinders that fit into the competitors"" locks and setting up key systems using their own keyway (grooving and slotting of the key and receiving plug, they lure the customer to buy their locks for future needs. Since in order for the new locks to fit in to the keying system they need to be the same keyway, the customer opts to buy their brand of lock for future use.
It has been desirable to add electronic security and access control features to mechanical locks since, for one thing, it is not possible to regulate the date, day and time of access using purely mechanical keys and meeting tumblers. Changing the combination of a lock when a key is compromised usually requires tumblers to be changed and all of the operating keys to be replaced which is costly. Also the number of unique combinations or permutations that can be achieved using purely mechanical keys and meeting tumblers is relatively low, and further security is often needed.
Many examples of purely electronic and electronic and mechanical combinations of control elements exist in the above referenced patents. Only a few of these inventions teach an instant replacement of the cylinder unit to fit to existing locks without further modification to the lock or the door. In most cases the cylinder unit acting as an electronic reader, having additional parts or components that are connected by wires to other parts of the lock or the door, requires modification of the door and/or the lock. These components generally are circuit boards containing decision-making electronics, batteries and electrically operated locking elements such as solenoids and motors. Providing a cylinder having electronic features that offers instant replacement to fit existing locks that work with a standard type of mechanical cylinders is desirable since there are millions of existing locks that can be easily retrofitted with the cylinders of these products. The prior art does not disclose a self contained cylinder wherein the cylinder is operated by a mechanical key with electronic features and electronic or electronic plus mechanical features of the key are relied on for access. These disclosed prior devices are operated by purely electronic keys (at times shaped like a conventional mechanical key) and do not offer mechanical key configuration on the key as an additional criteria for access or to be used on other mechanical only cylinders. Relying on the mechanical configuration of the key in addition to the electronic criteria is desirable because this offers additional security. Relying on the electronic criteria only of the key is sometimes also desirable as it provides flexibility.
In a facility not all doors may require access control i.e. regulating time and day of the entry. These doors may be operated by only the mechanical criteria of the key, not relying on the electronic criteria. It is also desirable because as mentioned above, installation of the electromechanical cylinders brings in sales of mechanical-only locks using the same keyway configuration used in the electromechanical cylinder.
Of those patents disclosing standard replacement cylinder units, Clarkson et al. U.S. Pat. No. 4,712,398 shows a cylinder operated by entirely electronic criteria. The key xe2x80x9cwhich closely resembles a traditional mechanical key without the usual bittingsxe2x80x9d contains electronic circuitry or memory in the key blade, which when inserted into the receiving cylinder, operates the cylinder if the data contained in the key matches the data stored in the receiving cylinder, by actuation of an electrically operated locking mechanism in the cylinder. Although there is one pin inside the cylinder and a single cut in the key, it is not used or relied on for granting access. It is used for centering and retention. All keys of the system have the same cut and all cylinders have the same pin, thus showing that no differentiation can be made between the keys requesting access based on mechanical configuration of the key. Clarkson employs a complicated communication scheme where the electronic identifying code is located on the key blade. Upon insertion of the key blade into the cylinder the key makes contact with its contact points xe2x80x9ckey connectorsxe2x80x9d to the cylinder""s contact points xe2x80x9ccylinder connectorsxe2x80x9d by brushing against each other to transfer the data from the key. Since the key electronics are located on the key blade itself, it is not possible to place a keyway profile (milling a grooving configuration) or cuts on the key.
Another similar system although not self contained disclosed in Chhatwal U.S. Pat. No. 5,337,588 (and also Chhatwal 5,507,162) employs an opto-electronic communication between the lock and the key for transmitting data contained in the key to the cylinder for requesting access. In addition the key makes physical contact with the cylinder unit via an isolated contact on the key blade to power the key electronics. The decision making electronics are located outside the cylinder and connected to the cylinder via a cable. Again the cylinder disclosed has a single pin which is used for alignment purposes. The physical size or shape of the pin and or matching cut in the key is not used for differentiating keys from one another, thus not constituting a mechanical key.
A cylinder disclosed by Spahn et al. U.S. Pat. No. 5,469,727 requires both mechanical and electronic elements to be present before granting access; however, the electronic circuitry and the power source are housed elsewhere in the lock and door and wired to the cylinder, requiring additional modification to the door and the lock, and thus defeating the purpose of instant replacement of a standard cylinder.
U.S. Pat. No. 5,140,317, Hyatt Jr. et al. also referenced above, discloses a combined mechanical lock/key combination which further includes an electronic feature for permitting opening of each lock in a system of similarly-keyed locks, only when authorized, and with a recording of each lock opening made. Although the system is not for locks using standard cylinders it is an example of prior art using both mechanical and electronic elements for granting access. The system disclosed in the patent includes a mechanical key with a key cut configuration, and with means for making electrical contact with electronics inside the lock. A separate box carried by the keyholder is connected by electric wiring to the key, the box including a keypad, a microprocessor, a battery for powering the system and the lock, and a memory with stored data. The lock includes a retractable blocking means which blocks opening of the lock""s bolt, separately from the mechanical bitting, except when prescribed conditions are met. When a solenoid in the lock is activated the blocking means is retracted. The lock also includes its own microprocessor, which controls switching of power to the solenoid, and with a memory within the lock storing data. The microprocessor within the lock compares coded data read from the key with coded data in the memory within the lock, and thus controls powering of the solenoid to situations in which a comparison, made within the lock""s microprocessor, determines that coded data read from the key matches coded data in the lock""s memory. The key (i.e. the separate box connected to the key) provides power to the lock""s solenoid to allow access. Also, the lock""s microprocessor further calculates a new code for the lock, after each opening of the lock.
The above patent is applicable to coin locks and other situations wherein a mechanical key has bitting matched to a large number of similar locks, but where control of the opening of each lock is desired, and where a record is needed of each lock""s opening. The system has been applied to pay telephone coin boxes. However, as noted, the system requires a separate box connected by electric wiring to the key, the box containing the equipment noted above. The system is thus unsuitable for applications wherein the key is used to access doors of a building or home as carrying a key along with a box is unacceptable. As stated above the system of the patent also requires additional hardware within the lock casing which defeats the purpose of instant replacement. In addition, considerable modification in retrofitting of existing locks is required, increasing cost of implementing the system, in addition to high cost of manufacture and materials.
A system described by the present application in U.S. Pat. No. 5,552,777, incorporated herein by reference, shows a lock system also applicable to coin locks and other situations wherein a mechanical key has bitting matched to a large number of similar locks, but where control of the opening of each lock is desired, and where a record is needed of each lock""s opening. This is an example of prior art using both mechanical and electronic elements of the key for granting access. The power, keypad, microcontroller and memory required for systems operation are incorporated into the key. This eliminates carrying of a box attached to the key. In addition the system of the patent also eliminates use of a microcontroller in the lock and combines the blocking means (solenoid) and the entire circuitry within the plug of a lock cylinder which allows instant replacement to existing locks as the lock described in the patented system is same size as the one it replaces. The key described in the U.S. Pat. No. 5,552,777 containing the keypad, microprocessor, memory and power source, although much smaller than the apparatus described by U.S. Pat. No. 5,140,317 (Hyatt, Jr. et al.), is still generally too large for applications wherein the key is used to access doors of a building or home.
All of the electronic and electromechanical cylinders provided as a replacement unit to the existing mechanical-only cylinders in the prior art are standardized cylinders such as mortise, rim and profile (euro-cylinder) cylinders. The prior art does not provide electronic or electromechanical cylinders for the bored type locks such as knob or lever locks and deadbolt locks.
It is an object of the invention described below to provide a self contained electromechanical lock cylinder which can be installed to lock""s existing cylinder cavity or cavities as its mechanical-only replacement and therefore easily retrofitted into existing locks used in doors of a building wherein a number of keys operate one or a number of locks, and which avoids the need for electronics, battery or other hardware which would take up space to be located inconveniently in the lock chassis or lock casing or attached to the door adjacent to the lock and wired to the cylinder. The lock cylinder is operated by a small size mechanical key carrying electronic properties, wherein the key is not larger than an ordinary car key and the mechanical and electronic properties of the key can be used simultaneously, or the electronic properties only can be used at some lock cylinders to grant access while the mechanical properties can be relied on for access at other doors where mechanical-only cylinders are used.
Another object of the invention is to provide a self contained knob or lever unit and a front housing for a deadbolt lock that will instantly retrofit bored type locks with electromechanical cylinders.
In additional aspects of the invention, it is an object to provide an access control system wherein the lock cylinders are programmable with the valid operating keys, in addition limiting the times and dates of the keys"" operation as well as providing means for some of the keys to work only a set number of times, and in another embodiment, to record each instance of access to a lock, by key number, in the situation of a lock accessible by a number of different keys. Another object of the invention is to provide easy to use programming methods for programming the cylinders.
In accordance with the present invention, a key and lock combination achieves the objectives of security in a door lock type system wherein a single or group of mechanical keys are fitted to a single or plurality of lock cylinders. The lock cylinders may or may not contain tumblers or other mechanical combination to be met by a mechanical key; in the case where they contain tumblers or other mechanical combinations, the cylinders may be similarly keyed or may be part of a master keying system. In the case that the cylinders to not contain tumblers or other mechanical combinations, they contain a keyway for accepting a mechanical key having a matching keyway.
The system of the invention includes a software program that runs in a personal computer which is used for programming of the locks and keys as well as performing management functions such as generating reports, audit trail, and adding more locks and keys to the system. The system of the invention includes a key as described in Gokcebay U.S. Pat. No. 5,367,295, which is self-contained, with a key head having memory and battery, as well as a contact point for a one wire bus connection with the lock, or a key with similar features but contact point(s) configured differently. The system also includes a programming key which can communicate with a computer that runs the system software via a serial port. When connected to the computer, the programming key is loaded with data for programming, reprogramming or auditing the locks in the system. Alternatively, communication from the computer to each lock, to identify valid key(s), permissible entry time, etc., can be made via radio frequency.
The lock cylinder of the invention includes an electrically operated blocking means which blocks the rotation of the cylinder plug. This electrically operated blocking means may be a solenoid, motor or another device which may be used alone or in combination to block the cylinder plug from turning.
The self contained electromechanical lock cylinder, which may be a mortise type, is installable into the existing cylinder cavity or cavities providing instant retrofit for existing locksets.
In one specific embodiment the mortise cylinder consists of two interconnectable parts. The first part is the cylinder unit, which has similar outside mechanical features to a typical mortise cylinder in its rear side and a modified front (face) side. The cylinder unit is installed in the cylinder cavity of the mortise lock and a cover unit slides over the face and attaches to the cylinder unit. The cylinder unit contains a typical rotatable cylinder plug with keyway for receiving a key and contains a one-wire bus connection for contact with the key, an electrically operated blocking means which prevents rotation of the plug independently of the mechanical bittings (shear plane tumblers), and a cylinder cam for engaging a latch or bolt mechanism of the lock when the cylinder is operated. The cover unit has a cavity which contains the power source and circuitry that includes a microcontroller which makes the decision to provide power to the electrically operated blocking means to release the cylinder plug only upon specified conditions being met. Also included is an EEPROM for storing access data, ports for connecting to an isolated surface for making connection with the auxiliary power in the case of power failure, LED and preferably buzzer for visual and sound indicators and a multi position connector for making contact with the cylinder unit""s connector. The cover unit also has another cavity to receive the front end of the modified cylinder unit wherein upon mating with the cylinder unit the face of the cylinder unit is flush with the outer surface of the cover unit. In the case of power failure, power can be applied externally to the cylinder via external terminals located on the exterior of the cover unit.
In another specific embodiment, the mortise cylinder consists of two connectable parts, the outside cylinder unit and the inside unit. The outside unit is in the size of a standard mortise cylinder containing the standard threading of a mortise cylinder and is installed into the outside cylinder cavity of the mortise lock, and the inside unit has a cylindrical section which is slightly smaller in diameter than the standard mortise cylinder and does not have threads and installs closely into the inside cylinder cavity of the mortise lock, even though that cavity will normally have threads. A rigid self-mating connector or a flex cable connector connects the outside and inside units to one another. The outside unit contains a typical rotatable cylinder plug with keyway for receiving a key and contains a one-wire bus connection for contact with the key, a electrically operated blocking means which prevents rotation of the plug independently of the mechanical bittings (shear plane tumblers), and a cylinder cam for engaging the latch or bolt mechanism of the lock when the cylinder is operated. The outside unit also has isolated terminals for making connection with auxiliary power in the case of power failure, preferably LED and buzzer for visual and sound indicators, and a multi position connector for making contact with the inside unit""s connector. The inside unit has a cavity containing the power source (battery) and circuitry which includes a microcontroller to make the decision to provide power to the electrically operated blocking means to release the cylinder plug only upon specified conditions being met, EEPROM for storing access data, and a multi position connector for making contact with the outside unit""s connector. In a specific embodiment the inside unit may also contain a rotatable cylinder plug with keyway for receiving a key, and other features similar to the outside cylinder: a one-wire bus connection for contact with the key, a electrically operated blocking means which prevents rotation of the plug independently of the mechanical bittings (shear plane tumblers), and a cylinder cam for engaging a latch or bolt mechanism of the lock when the cylinder is operated. This will accommodate situations wherein a cylinder is required in both sides of the lock or alternatively it may contain a thumb-turn unit for engaging the lock from inside.
The self-contained electromechanical lock cylinder, which may be a rim type, is installable into the existing cylinder cavity or cavities providing instant retrofit for existing locksets or exit devices.
In one specific embodiment the rim cylinder consist of two interconnectable parts, as in the mortise cylinder described above. The first part is the cylinder unit, the second part is the cover unit. The cylinder unit has the same outside mechanical features of a typical rim cylinder in its rear side and a modified front (face) side. The cylinder unit is installed in the cylinder cavity of the rim lock and the cover unit slides over the face and attaches to the cylinder unit. Preferred features are similar to those listed above.
Another specific embodiment of the electromechanical lock cylinder of the invention is in a profile type cylinder installable into an existing cylinder cavity or cavities providing instant retrofit for existing profile cylinder locksets. Preferred features are similar to those described above.
In another embodiment of the invention a self-contained knob or lever unit containing an electromechanical cylinder is provided for replacing the existing knob or lever unit of a mechanical lock. The self contained knob or the lever unit installs on to the knob or lever receptacle of the existing lock. The mechanical-only knob or lever is removed and is replaced with the self-contained knob or lever unit. The self-contained knob or lever unit allows for instant conversion of the mechanical lock to a electromechanically operated lock. In a preferred embodiment the self contained knob or lever unit has features similar to those described above in other embodiments of electromechanical cylinders. The self contained knob or lever unit has a cavity which contains the power source (battery) and circuitry including a microcontroller which makes the decision to provide power to the electrically operated blocking means to release cylinder plug only upon specified conditions being met, EEPROM for storing access data, ports for connecting to an isolated surface for making connection with the auxiliary power in the case of power failure, preferably LED and buzzer for visual and sound indicators and a multi position connector for making contact with the cylinder unit""s connector, all as described above. In the case of power failure, power can be applied externally to the cylinder via external terminals located on the face of the knob or lever unit.
In all five described embodiments a decision to grant access is made by the microcontroller by comparing the data read from the key requesting access with the data in the lock""s database. Within the lock""s database is a list of keys, by serial number or code, which are within the system and have mechanical characteristics that match the mechanical characteristics of the lock. If the serial number or code of the key requesting access exists within the lock""s database of serial numbers or codes, with matching of any other criteria which may be programmed (i.e. day of the week or specific time slot, number of times etc.) are met, the access is granted by the microcontroller by supplying power to the solenoid. Upon release of the electrically operated blocking means and shearline created by the matching mechanical configuration of the key to the cylinder, the plug is free to rotate to perform a conventional unlocking action. An LED indicator may also light to show that the cylinder is ready to turn and a buzzer may be used to provide sound indicator for the operation.
In another specific embodiment, the cylinder described above does not contain mechanical bittings and upon release of the electrically operated blocking means the cylinder plug is free to rotate to perform a conventional unlocking action.
In another embodiment, the shearline is created by movement of the locking member indirectly by the release of the solenoid. In this embodiment the solenoid with the power of its spring moves a locking member in a shape of a flat wafer upwards blocking the shearline. The tip of the solenoid""s plunger is conic shaped and in its unpowered mode moves the locking wafer by riding on a hole of the wafer by the force of its plunger spring. The wafer is spring loaded with a small spring which in its relaxed condition keeps the wafer away from the shearline; however, since the plunger spring is more powerful than the wafer""s spring the wafer blocks the shearline. Upon powering of the solenoid the plunger is pulled in, leaving the wafer spring to move the wafer away from the shearline, allowing the cylinder plug to turn. The wafer hole is oval shaped to allow the retraction of the solenoid plunger even is pressure is applied to the cylinder plug from a prematurely turning key.
The one wire bus connection in the cylinder plug may be generally as disclosed in the above-referenced U.S. Pat. No. 5,367,295, and may have a spring-biased, isolated contact which extends forward from a bore in the cylinder plug; alternatively, the isolated contact may be flush with the plug or recessed, so long as the key""s contact reaches the lock""s contact. The metal of the cylinder plug forms a ground connection. The one wire bus connection is generally used for the system for communicating data between the key and the cylinder; however, in some cases power may also be supplied to the cylinder by a programming key or another special functioning key for powering the cylinder""s electronic circuitry and locking solenoid if the power source of the cylinder fails. The isolated contact described above extending from the cylinder plug may also be located on the cylinder shell, with the relocation of the meeting isolated contact on the key. Alternatively both ground and data contacts on the key could be isolated, meeting the contacts on the cylinder.
The microcontroller which makes the decision to provide power to the solenoid to release the blocking pin only upon specified conditions being met, the EEPROM for storing access data and related circuitry alternatively could be housed within the cylinder shell with or without the electrically operated blocking mechanism such as a solenoid or motor.
In one preferred embodiment the access data is programmed via a programming key which is recognized by the cylinder, and the new programming data is uploaded to the cylinder. The programming data is first loaded to the programming key through the serial port of the computer that is running the system software. When the key is inserted into the cylinder the cylinder reads the relevant programming data for itself and marks the section of the programming key that carried the data for the particular cylinder as read. When the programming key is returned to the computer that is running the system software the programming key is read by the system software via the computer""s serial port to verify that the programming is complete for the particular cylinder or cylinders. Alternatively, the programming of the cylinders could be accomplished by insertion of the programming key into a lock cylinder followed by the insertion of the keys followed by the insertion of the programming key. Inserting the operating keys in the window between the first insertion of the programming key and the second insertion of the programming key allows the programming of the lock for the operating keys.
In a preferred embodiment, the opening of each lock is recorded by the microcontroller, in the data storage of the circuitry for audit trail purposes. Depending on the available space or preference, approximately the last 20 entries may be kept in the lock""s data storage. Each lock ID in the database is marked as having been opened when that event has occurred, and preferably the time and date are also marked. In the case of a need for audit trail the programming key retrieves the data of the last entries from the lock, uploads the data to the system software running in the personal computer via the serial port of the computer, and prints this information in the system printer. The data includes the keys that have had access as well as attempted lock openings.
The said system software provides a three dimensional matrix that contains the access data for the cylinders including the dates and times when the access is permitted to particular keys or keyholders. This data is loaded on to a programming key which is subsequently entered into the cylinder to upload the access data.
The relating of the access data to the cylinders of the system can also be done via a small radio which is plugged in or otherwise attached to the cylinder of the invention. In this case the access data resides in the system computer, and when a key is inserted to the cylinder the identification of the key is read by the cylinder, which then requests an access decision from the computer. The cylinder waits for the answer and grants access based on the response from the computer.
The cylinders that contain mechanical combinations may be rekeyed or otherwise re-combinated in the manner of typical mechanical lock cylinders, refitting the mechanical bitting (new sets of tumblers). Locks may also be masterkeyed to provide or limit access based on the mechanical configuration of the tumblers.
It is thus seen that the mechanical/electronic lock and key of the invention provides, in an extremely compact fashion, electronic access control to a conventional mechanical lock. No additional space in a lock is required to implement the system of the invention. The system is particularly useful where a number of keys are matched to a number of locks such as office building, hospitals, colleges, homes and apartments. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.